Field
The disclosed concept relates to electrical switching apparatus, such as, for example, circuit breakers. The disclosed concept also relates to housing assemblies for circuit breakers.
Background Information
Electrical switching apparatus include, for example, circuit switching devices; circuit interrupters, such as circuit breakers; network protectors; contactors; motor starters; motor controllers; and other load controllers. Circuit breakers are used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition or a relatively high level short circuit or fault condition.
For small power switches, which are commonly referred to as miniature circuit breakers, and which are used, for example, in residential and light commercial electrical distribution systems, the connector assembly for electrically connecting the power conductor of the miniature circuit breaker to the electrical conductors (e.g., without limitation, wires; cables) of the distribution system typically includes a collar terminal. Specifically, for example, the power conductor of the miniature circuit breaker is a relatively rigid, flat conductor, and the collar terminal generally includes a cylindrical or square body having a transverse slot in which the flat power conductor of the circuit breaker and the wire or cable are received, and a tapped bore into which a terminal screw is threaded to clamp the wire or cable against the power conductor and to secure the collar to the power conductor. Typically, the collar is disposed in a recess at a corresponding end of the circuit breaker molded housing. Because tightening the terminal screw of the collar places relatively large amounts of torque on the housing, it is necessary for the housing to be strong.
Additionally, circuit breakers typically include a set of separable electrical contacts. The separable electrical contacts are in physical and electrical contact with one another when it is desired that the circuit breaker energize a power circuit. When it is desired to interrupt separable electrical contacts, an electrical arc is formed in the space between the contacts. The arc provides a means for smoothly transitioning from a closed circuit to an open circuit, but needs to be properly extinguished. In order for the circuit breaker to be properly certified, such as, for example and without limitation, to be properly certified by Underwriters Laboratories Inc., headquartered in Northbrook, Ill., the circuit breaker must be able to interrupt predetermined currents without failing. During the testing, it is critical that the housing of the circuit breaker have good gassing characteristics in order to be able to properly extinguish the arc.
Some known housing materials have the requisite strength to be able to withstand the torque that results from tightening and loosening the terminal screw of the collar, but lack the necessary gassing characteristics to effectively extinguish the arc. Other known housing materials have the necessary gassing characteristics to extinguish the arc, but lack the requisite strength to be able to withstand the torque that results from tightening and loosening of the terminal screw.
There is thus room for improvement in electrical switching apparatus and in housing assemblies therefor.